Shincheonji only targets other Christians from churches and sheep-steals.
It is true that believers living at the time of Revelation must enter Jesus’ field to carry out the work of harvest. Jesus came at the First Coming for the lost sheep of Israel. He returns to gather his sheep to his Kingdom (Matthew 25, Revelation 7, Revelation 14, Revelation 21).
But it is also true that at Shincheonji you will find people from all sorts of backgrounds culturally and even faith-wise too. I had people in my group that were Buddhist, Hindu, non-believers, etc. It was an interesting mix of people and they had individually good stories of why they came to faith in God after learning from Shincheonji.
Shincheonji also does a lot in emphasizing religious unity and interfaith dialogue. We got to go these events where religious leaders would speak about different topics and how their faith viewed them or answered those important life questions.